Concrete stressing apparatus and remote control unit therefor



Sept. 30, 1969 D. v. KRANTZ 3,469,399

CONCRETE STRESSING APPARATUS AND REMOTE CONTROL UNIT THEREFOR I Filed Feb. 16. 1968 2 Sheets-Sheet 1 iii MIN

Sept. 30, 1969 p. v. KRANTZ 3 9 CONCRETE STBESSING APPARATUS AND REMOTE CONTROL UNIT THEREFOR Filed Feb. 16. 1968 2 Sheets-Sheet 2 REMOTE CONTRO $5. EN EMQ UM c a 1 12am p M V2 F I i M United States Patent Office Patented Sept. 30, 1969 US. CI. 60-52 8 Claims ABSTRACT OF THE DISCLOSURE Apparatus for stressing tendons in concrete including a pumping unit having a de-tensioningvalve in fluid communication with a hydraulic jack and a portable or stationary remote control de-tensioning unit having a means thereon for activating the pumping unit and for actuating the de-tensioning valve whereby the pressure in the jack can be released under precise and full control and tension on the tendons can be gradually reduced.

Background of the invention The field of the invention relates to an apparatus used in the process of pre-tensioning or post-tensioning tendons in concrete and a means for reducing the tensile stress on the tendons after initial overstressing to a predetermined lower tensile stress.

In a conventional post-tensioning operation, tendons are stretched a predetermined amount and shims are positioned in place. The tension is then released and the tendons are allowed to snap back thereby putting the concrete in a state of compression. When the tendons are allowed to snap back rapidly there is an impact release effect on the tendons which prevents the tendons from having a normal tendency to return to a predetermined stressed state thereby reducing the efiectiveness of the stressing operation.

The subject invention seeks to obviate the impact release efiect by providing a de-tensioning means with an accurate digital read-out which is capable of gradually releasing tension on the strands.

Summary of the invention It is an object of this invention to provide an apparatus for stressing tendons and a remote control unit therefor.

It is a further object of the invention to provide a detensioning unit having an accurate digital read-out means for reading the pressure exerted by a jack on tendons.

Another object of the invention is to provide a stressing apparatus which is versatile in its use and efficient in operation. I

In carrying out the invention, in one form an apparatus for stressing tendons is provided including a pumping unit comprising a motor-driven pump, a directional control valve in fluid communication with the pump unit and operable remote therefrom, a de-tensioning valve in fluid communication with the directional control valve; hydraulic jack means in fluid communication with the pump unit, said jack means fluidly cooperating with the directional control and the de-tensioning valve; the improvement comprising a remote control de-tensioning unit electrically connected to the motor-driven pump and the directional control valve for activating the pump and the directional control valve, the de-tensioning unit having a means therein connected to the de-tensioning valve for reducing the pressure in the jack means and a readout means for reading the pressure.

Brief description of the drawing FIGURE 1 is a perspective view of the stressing apparatus embodying the invention;

FIG. 2 is an enlarged 'view, partly broken away, of the remote control de-tensionin g unit;

FIG. 3 is a schematic view of the apparatus with a directional control valve shown in one position;

FIG. 4 is a schematic view of the apparatus with the directional control valve shown in a second position;

FIG. .5 is a schematic view of the apparatus of FIG. 3 with the de-tensioning lever and valve shown in the op erational position; and

FIG. 6 is a schematic view of the apparatus with the directional control valve shown in a third position.

Description of the preferred embodiment Referring more particularly to the drawing, an apparatus for stressing tendons is shown in FIG. 1 including a pumping unit 10, a hydraulic jack 11 in fluid communication with the pump unit and a remote control de-tensioning unit 12. Inlet and outlet hoses 13 and 14, respectively, interconnect jack 11 with pump unit 10 in the conventional manner. Remote control de-tensioning unit 12 is electrically connected to pump unit 10 by a cable 15 which extends therebetween. Cable 15 is conventionally connected to a solenoid valve and a motor driven pump, both of which are housed within the pumping unit. The operation of the valve and the motor driven pump will be discussed later in detail.

In FIG. 2, the remote control de-tensioning unit is shown in detail and comprises a generally rectangular box 16 housing a de-tensioning mechanical linkage system 18, a digital read-out system 19, and control buttons 20, 21 and 22.

The mechanical linkage system 18 may be of the type manufactured by the American Chain & Cable Company and comprises a ring gear 23 mounted on shaft 24, a pinion gear 25 mounted on shaft 26 and adapted to cooperate with ring gear 23, handle 27 rigidly attached to shaft 26, and safety stops 28 and 29 for limiting the rotation of ring gear 23. A cable 30 is disposed in groove 31 in ring gear 23 and is rigidly attached at one end to said ring gear. One end 32 of the cable is disposed in aperture 33 in a spoke 34 and the other end extends from ring gear 23 to a de-tensioning valve in the pumping unit where it is conventionally connected. The valve may be opened or closed by rotating handle 27 counterclockwise or clockwise, respectively.

The digital read-out system 19 may be of the type manufactured by the United System Corporation and is suitably mounted in box 16. A pressure transmitter (not shown) is suitably mounted in the pumping unit and is used to convert the hydraulic pressure into a proportional D.C. electrical signal. The signal is fed to the read-out system where the pressure exerted by the jack on the tendons is readable in pounds per square inch within an accuracy of plus or minus /2 of 1% over a 20,000 psi. range. It has been found that the actual read-out accuracy is substantially higher than that of the conventional pointer-type instrument.

As shown in FIG. 2, there are three control buttons on the remote control de-tensioning unit 12. Control button 20 is the start button and is electrically connected to a motor in pump unit 10 in the conventional manner. Control button 21 is the stop button and is similarly connected to the pump unit. Control button 22 is a springreturn to neutral selector switch which controls the directional control valve in the pumping unit. The switch has three positions, namely (1) the forward position; (2) the reverse position; and (3) the neutral or hold position.

The operation of the apparatus will now be described with reference to FIGURES 3-6. In FIG. 3, a schematic view of the apparatus is shown wherein pressure is being applied so as to force the cylinder in a downward direction. Oil is pumped by pump P driven by motor M from reservoir R through ports B and A of the directional control valve DCV and into the jack as shown by the arrows. The de-tension valve DV is closed and oil in the head end of the jack flows through ports C and D of directional control valve DCV and through filter F into reservoir R. The selector swit h on the de-tensioning unit is manually held in the forward position during the tensioning operation; A safety relief valve V is inserted in the system and is designed to open automatically if the pressure in the jack exceeds the safe upper limit of the system which in normal operation will be up to 10,000 psi.

After a predetermined pressure has been reached as indicated by the digital read-out system in the de-tensioning unit, the directional control valve is allowed to spring back to neutral and the pressure in the jack is held constant after stabilization. FIGURE 4 shows the position of the directional control valve when the selector switch is turned to neutral. Port A is blocked and the pressure in the jack is held constant. Oil from the head of the jack fiows'through ports C and D and back to reservoir R. Pump P continues to pump oil from the reservoir through ports B, C and D and back to the reservoir as indicated by the arrows.

The de-tensioning operation is shown in FIG. 5 wherein de-tension valve DV is opened by manual actuation, i.e. by turning handle 27 in a counterclockwise direction on the remote control unit. As the valve opens, the oil is metered from the pressurized end of the jack back to the reservoir. The valve is preferably a fine needle valve of the type manufactured by Manatrol (MV-400 series) and is capable of precisely regulating the amount of fluid flow so as to allow a controlled release of pressure and elongation of the tendons. The controlled release prevents a reduction of the stressing effect which would be present if the tendons were allowed to snap back.

In FIG. 6, a schematic view of the apparatus is shown depicting the directional control valve in its position for the return of the jack. Oil is pumped from reservoir R through ports B and C of directional control valve DCV and into the head end of the jack. Oil from the opposite end of the jack flows through ports A and D of directional control valve DCV and into the reservoir. As the piston rod bottoms out and the pump continues to operate, a pressure is built up to a predetermined low pressure setting of normally between 250 and 750 psi. on a low pressure relief valve V This valve opens when the pressure reaches the predetermined setting and allows the oil to flow back to the reservoir thereby preventing the pump or motor from burning out and preventing blowing of the seals of the jack due to excessive pressures.

Preferably, the directional control valve is a four-way, r

three-position double solenoid operated valve having a valve body designed to slide into one of the three positions within a cylindrical valve housing. The valve could, alternatively, be hydraulically or mechanically actuated. When the selector switch is turned to forward the valve body slides to one position shown in FIG. 3, and conversely when the switch is turned to reverse the valve body slides to another position. The third position of the valve body is the neutral or hold position.

The de-tension valve DV may be regulated at the pump unit by manually operating lever 32. This adds an additional safety feature since the release of pressure can be effected either at the remote control unit 12 or at the pump unit.

It will be understood that a conventional recorder could also be connected to the pressure transmitter to record the pressure. For example, a digital recorder or an X-Y recorder could be used.

An advantage in using a mechanical de-tensioning system is that in the event of power failure the directional control valve would shift to the neutral position and the pressure would be held constant. Electrical repairs could be made or the pressure could be gradually released by manually turning the de-tension handle in a counterclockwise direction. It will be understood that an electrical or hydraulic system could be used to actuate the de-tension valve, however, the advantage discussed above in using a mechanical system may be lost.

It is thus seen that a stressing apparatus has been provided having a means for controlling the tension on the tendons which is capable of accurately recording the tension and which is versatile and efiicient in operation.

While a particular embodiment of the invention has been shown, it isto be understood that the invention is not limited thereto since many minor modifications may be made; and it is, therefore, contemplated by the appended claims to cover any'such modifications as fall within the true spirit and scope of the invention.

The invention having thus been described, what is claimed and desired to be secured by Letters Patent is:

1. In an apparatus for stressing tendons in concrete including a pumping unit comprising a motor drivenpump, a directional control valve in fluid communication with the pump unit and operable remove therefrom, a de-tensioning valve in fluid communication with said directional control valve; hydraulic jack means in fluid communication with said pump unit, said jack means fluidly cooperating with said directional control valve and said de-tensioning valve; the improvement comprising a remote control de-tensioning unit electrically connected to said motor driven pump and said directional control valve for activating the pump and the directional control valve, said de-tensioning unit having a means therein connected to said detensioning value in the pumping unit for controlled reduction of the pressure in the jack means.

2. The invention according to claim 1 wherein the directional control valve is a three-position, double solenoid operated valve and the remote control de-tensioning unit has a three-position switch mounted therein electrically connected to said directional control valve.

3. The invention according to claim 1 wherein the detensioning unit further includes a digital read-out means mounted therein for reading the pressure exerted by the jack means during the tensioning and de-tensioning operation.

4. The invention according to claim 1 wherein the detensioning valve is connected to said means in the de-tensioning unit by a mechanical linkage whereby the de-tensioning can be effected manually.

5. The invention according to claim 1 wherein the pumping unit includes at least one safety relief valve in fluid communication with said jack means for relieving overpressure in said jack means.

6. The invention according to claim 5 wherein the directional control valve is a three-position, double solenoid operated valve and the remote control de-tensioning unit has a three-position switch mounted therein electrically connected to said directional control valve.

7. The invention according to claim 5 wherein the detensioning unit further includes a digital read-out means mounted therein for reading the pressure exerted by the jack means during the tensioning. and de-tensioning operation.

8. The invention according to claim 5 wherein the detensioning valve is connected to said means in the de-tensioning unit by a mechanical linkage whereby the de-tensioning can be effected manually.

References Cited UNITED STATES PATENTS 2,323,519 7/1943 Dean.

2,611,246 9/1952 Ackerman.

3,036,356 5/1962 Greulich 52 -223 XR 3,070,954 1/1963 Basso.

EDGAR W. GEOGHEGAN, Primary Examiner U.S ci. X.R.

" UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 69,399 Dated September 30, 1969 Inventor) Donald Victor Krantz If is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1: Column 4, line 20, "remove" should be remote Claim 1': I Column 4, line 30, "value'! should be valve onGNED ANu SEALED DEB 2 3 m (SEAL) Amen Ed Fletcherjr' v WILLIAM E, JR. Attesting Officer Commissioger o1 Patents 

